# Multiple choice question for engineering

## Set 1

1. For a transistor amplifier to be stable, either the input or the output impedance must have a real negative part.

a) True

b) False

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2. ____________ condition, if met then the transistor can be impedance matched for any load.

a) Conditional stability

b) Unconditional stability

c) Infinite gain

d) Infinite input impedance

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3. A network is said to be conditionally stable if:

a) │Гin│<1, │Гout│<1.

b) │Гin│>1, │Гout│>1

c) │Гin│>1, │Гout│<1

d) │Гin│<1, │Гout│>1

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4. Stability condition of an amplifier is frequency independent and hence can be operated at any frequency.

a) True

b) False

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5. For a unilateral device condition for unconditional stability in terms of S parameters is:

a) │S_{11}│<1, │S_{22}│<1

b) │S_{11}│>1, │S_{22}│>1

c) │S_{11}│>1, │S_{22}│<1

d) │S_{11}│<1, │S_{22}│>1

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_{11}│<1, │S

_{22}│<1. S

_{11}parameter signifies the amount of power reflected back to port 1, which is the input port of the transistor. If this S parameter is greater is than 1, more amount of power is reflected back implying the amplifier is unstable.

6. If │S_{11}│>1 or │S_{22}│>1, the amplifier cannot be unconditionally stable.

a) True

b) False

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_{11}│>1 or │S

_{22}│>1, the amplifier cannot be unconditionally stable because we can have a source or load impedance of Zₒ leading to Гs=0 or ГL=0, thus causing output and input reflection coefficients greater than 1.

7. For any passive source termination ГS, Unconditional stability implies that:

a) │Гout│<1

b) │Гout│>1

c) │Гin│<1

d) │Гin│>1

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^{jφ}.

8. The condition for unconditional stability of a transistor as per the K-∆ test is │∆│> 1 and K<1.

a) True

b) False

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9. If the S parameters of a transistor given are

S_{11}=-0.811-j0.311

S_{12}= 0.0306+j0.0048

S_{21}=2.06+j3.717

S_{22}=-0.230-j0.4517

Then ∆ for the given transistor is:

a) 0.336

b) 0.383

c) 0.456

d) None of the mentioned

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_{11}S

_{22}-S

_{12}S

_{21}│. Substituting the given values in the above equation, the ∆ of the transistor is 0.336.

10. By performing the K-∆ test for a given transistor the values of K and ∆ were found to be equal to 0.383 and 0.334 respectively. The transistor with these parameters has unconditional stability.

a) True

b) False

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## Set 2

1. Which mode of propagation is supported by a strip line?

a) TEM mode

b) TM mode

c) TE mode

d) None of the mentioned

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2. The higher order wave guide modes of propagation can be avoided in a strip line by:

a) Restricting both the ground plate spacing and the sidewall width to less than λ_{d}/2

b) Restricting both the ground facing plate spacing and the sidewall width to less than λ_{d}

c) Filling the region between 2 plates with di electric

d) Restricting both the ground plate spacing and the sidewall width between λ_{g} and λ_{g}/2

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_{d}/2.

3. Stripline can be compared to a:

a) Flattened rectangular waveguide

b) Flattened circular waveguide

c) Flattened co axial cable

d) None of the mentioned

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4. If the dielectric material filled between the round plates of a microstrip line has a relative permittivity of 2.4, then the phase velocity is:

a) 1.3*10^{8} m/s

b) 1.9*10^{8} m/s

c) 3*10^{8} m/s

d) 2*10^{8} m/s

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^{8}m/s.

5. Expression for propagation constant β of a strip line is:

a) ω(√µ∈∈_{r})

b) ω(√µₒ/√∈_{r})

c) ω/(√µₒ∈ₒ∈_{r})

d)c/(√µₒ∈ₒ∈_{r})

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_{r}).

6. If the phase velocity in a stripline is 2.4*10^{8}m/s, and the capacitance per unit length of a micro stripline is 10pF/m, then the characteristic impedance of the line:

a) 50 Ω

b) 41.6 Ω

c) 100 Ω

d) None of the mentioned

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_{P}c). Substituting the given values of phase velocity and capacitance, the characteristic impedance of the line is 41.6 Ω.

7. The expression for characteristic impedance Zₒ of a stripline is:

a) (30πb/√∈_{r})(1/W_{e}+0.441b)

b) (30πb) (1/W_{e}+0.441b)

c) 30π/√∈_{r}

d) (1/W_{e}+0.441b)

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_{r})(1/W

_{e}+0.441b).

8. If the effective width of the center conductor is 3 mm and the distance between the two ground plates is 0.32 cm with the material of the dielectric used having a relative permittivity of 2.5, then what is the characteristic impedance of the strip line?

a) 50Ω

b) 71.071Ω

c) 43.24Ω

d) 121Ω

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_{r})(1/W

_{e}+0.441b). Substituting the given values in the given expression and hence solving, the characteristic impedance of the line is 43.24 Ω.

9. The wave number of a stripline operating at a frequency of 10 GHz is:

a) 401

b) 155

c) 206

d) 310

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_{r}/c, c is the speed of light in space, ∈r is the relative permittivity of the dielectric medium. Substituting the given values in the equation, the wave number is 310.

10. If the loss tangent is 0.001 for a stripline operating at 12 GHz with the relative permittivity of the dielectric material being used equal to 2.6, then the conductor loss is:

a) 0.102

b) 0.202

c) 0.001

d) 0.002

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_{r}/C which is the wave number. Substituting the values in the above two equations, conductor loss is 0.202.

11. If the dielectric material used between the grounded plates of a stripline is 2.2, when the strip line operating at 8 GHz, the wavelength on stripline is:

a) 1.2 cm

b) 2.52 cm

c) 0.15 cm

d) 3.2 cm

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_{r}. substituting in the above relation, the propagating wavelength on the microstrip line is 2.52 cm.

12. Fields of TEM mode on strip line must satisfy:

a) Laplace’s equation

b) Ampere’s circuital law

c) Gaussian law

d) None of the mentioned

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## Set 3

1. If an antenna has a directivity of 16 and radiation efficiency of 0.9, then the gain of the antenna is:

a) 16.2

b) 14.8

c) 12.5

d) 19.3

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2. Gain of an antenna is always greater than the directivity of the antenna.

a) True

b) False

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3. A rectangular horn antenna has an aperture area of 3λ × 2λ. Then the maximum directivity that can be achieved by this rectangular horn antenna is:

a) 24 dB

b) 4 dB

c) 19 dB

d) Insufficient data

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4. A rectangular horn antenna has an aperture area of 3λ × 2λ. If the aperture efficiency of an antenna is 90%, then the directivity of the antenna is:

a) 19 dB

b) 17.1 dB

c) 13 dB

d) 21.1 dB

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5. If an antenna has a directivity of 16 and is operating at a wavelength of λ, then the maximum effective aperture efficiency is:

a) 1.27λ^{2}

b) 2.56λ^{2}

c) 0.87λ^{2}

d) None of the mentioned

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^{2}/4π, D is the directivity of the antenna. Substituting in the equation the given values, the maximum effective aperture is 1.27λ

^{2}.

6. A resistor is operated at a temperature of 300 K, with a system bandwidth of 1 MHz then the noise power produced by the resistor is:

a) 3.13×10^{-23} watts

b) 4.14×10^{-15} watts

c) 6.14×10^{-15} watts

d) None of the mentioned

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^{-15}watts.

7. With an increase in operating frequency, the background noise temperature:

a) Increases

b) Decreases

c) Remains constant

d) Remains unaffected

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8. The noise temperature of an antenna is given by the expression:

a) radTb + (1-rad) Tp

b) (1-rad) TP

c) radTb

d) None of the mentioned

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9. Low is the G/T ratio of an antenna, higher is its efficiency.

a) True

b) False

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10._________ has a constant power spectral density.

a) White noise

b) Gaussian noise

c) Thermal noise

d) Shot noise

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## Set 4

1. A single section tapered line is more efficient in impedance matching than a multisection tapered line for impedance matching.

a) True

b) False

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2. Passband characteristics of tapered lines differ from one type of taper to another.

a) True

b) False

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3. For a continually tapered line, the incremental reflection co-efficient is:

a) ∆Z/2Z

b) 2Z/∆Z

c) ∆Z_{0}/2Z_{0}

d) None of the mentioned

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4. The variation of impedance of an exponentially tapered line along the length of the line is given by:

a) Z(z)=Z_{0}e^{az}

b) Z(z)=Z_{0}e^{-az}

c) Z(z)=Z_{0}e^{2az}

d) Z(z)=Z_{0}e^{-2az}

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_{0}e

^{az}. The constant ‘a’ is defined as L-1 ln(Z

_{L}/Z

_{0}).

5. The value of constant ‘a’ for an exponentially tapered line of length 5 cm with load impedance being 100Ω and characteristic impedance of the line is 50Ω is:

a) 0.1386

b) 0.265

c) 0.5

d) 0.2

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6. Reflection co-efficient magnitude response is an exponential curve for tapered line.

a) True

b) False

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7. Triangular taper is the best solution for any impedance matching requirement.

a) True

b) False

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8. The maximum passband ripple in a Klopfenstein taper matching section is:

a) Г_{0}/cos h A

b) Г_{0}/sin h A

c) Г_{0}/ tan h A

d) None of the mentioned

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_{0}/cos h A. Here, Г

_{0}is the reflection co-efficient at zero frequency. A is a trigonometric function relating reflection co-efficient at zero frequency and maximum ripple in the passband.

9. For any load impedance, perfect match can be obtained and the minimum reflection co-efficient achieved can be zero.

a) True

b) False

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10. For a given load (a fixed RC product), a broader bandwidth can be achieved with a low reflection co-efficient in the passband.

a) True

b) False

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11. A perfect match can be obtained in the passband for any impedance matching circuit around the center frequency for which it is defined.

a) True

b) False

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## Set 5

1. When a lossless line is terminated with an arbitrary load impedance Z_{L}, then it :

a) causes wave reflection on transmission lines

b) transmits the entire supplied power

c) causes loss in transmission line

d) none of the mentioned

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2. We say a transmission line is matched when:

a) Z_{L}=Z_{0}

b) Z_{L}=√Z_{0}

c) Z_{L}=Z_{0}/2

d) Z_{L}=2Z_{0}

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_{L}=Z

_{0}.

3. Voltage reflection coefficient can be defined as:

a) ratio of amplitude of reflected voltage wave to the transmitted voltage wave

b) ratio of amplitude of reflected voltage to the incident voltage wave

c) ratio of load impedance to the characteristic impedance of the transmission line

d) none of the mentioned

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4. Expression for a voltage reflection co-efficient in terms of load impedance and characteristics impedance is:

a) (Z_{L}– Z_{0})/(Z_{L}+ Z_{0})

b) (Z_{L}+ Z_{0})/(Z_{L}– Z_{0})

c) Z_{L}. Z_{0}/( Z_{L}+ Z_{0})( Z_{L}-Z_{0})

d) (Z_{L}+ Z_{0})( Z_{L}-Z_{0})/ Z_{L}. Z_{0}

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5. If a transmission line of a characteristics impedance 50 Ω is terminated with a load impedance of 100 Ω, then the reflection co efficient is:

a) 0.3334

b) 0.6667

c) 1.6

d) 1.333

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_{L}– Z

_{0})/(Z

_{L}+ Z

_{0}) .substituting the given values of load and characteristic impedance, we get reflection co-efficient equal to 0.3334.

6. Return loss for a transmission line in terms of its reflection co efficient is given by:

a) -20logl┌l in dB where ┌ is the reflection coefficient.

b) -10logl┌l in dB where ┌ is the reflection coefficient

c) -10log (1/l┌l) in dB where ┌ is the reflection coefficient

d) -20log (1/l┌l) in dB where ┌ is the reflection coefficient

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7. If the reflection coefficient for transmission line is 0.24, then the return lossin dB is:

a) 12.39dB

b) 15dB

c) -12.39dB

d) -15.2dB

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8. Expression for VSWR in terms of reflection co-efficient is:

a) (1+│┌│)/(1-│┌│)

b) (1-│┌│)/(1+│┌│)

c) 1/│┌│

d) 1/1+│┌│

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9. If the reflection co-efficient for a transmission line is 0.3, then the VSWR is:

a) 0.5384

b) 1.8571

c) 0.4567

d) 3.6732

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10. If a transmission line of characteristic impedance 50 Ω is terminated with a load impedance of 150 Ω , then VSWR is:

a) 0.75

b) 0.5

c) 2

d) none of the mentioned

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_{L}– Z

_{0}/Z

_{L}+ Z

_{0}. Substituting for Z

_{L}and Z

_{0}in the above equation, VSWR is 0.5.